1. Field of the Invention
The present invention relates to a sludge dehydration device and, more particularly, to a device provided with belts to press and dehydrate the sludge.
2. Description of the Prior Art
A large amount of concentrated sludge, having a large amount of water contained therein, is produced at sewage treatment plants and other various industrial discharge treatment plants. This concentrated sludge is not dumped away as is and, therefore, a dehydration device must be equipped to dehydrate the sludge further. To provide for such further dehydration, there conventionally have been used dehydration devices of the belt press type which place the concentrated sludge between two sheets of belts to press and dehydrate it into dehydrated cakes. FIG. 1 shows an example of the previously known belt press type dehydration devices.
Referring to FIG. 1, an endless lower belt 1 and an upper belt 2 composed of filter sheets are driven at the same speed. Concentrated sludge A is supplied onto the lower belt 1 from a chute 3. The concentrated sludge is conveyed by the lower belt 1 and is forced between the lower belt 1 and the upper belt 2 where the sludge is pressed by multiple drums 4. By this pressure the concentrated sludge A is dehydrated by pressing water through both belts 1 and 2 and the sludge is made into dehydrated cakes A'. The cakes A' are scraped from each of the belts 1 and 2 by the scrapers 5 and 6.
Thus, in the previously known dehydration devices of the belt press type, the belts are laid on the rollers 7 and 8 and over the press drums 4 and are driven by the tension of the belts. Accordingly, both the upper belt 2 and lower belt 1 must be provided with sufficient tensile strength to withstand the tension imposed by the other components. Therefore, previously known belts 1 and 2 are composed of closely woven, thick filter sheets in order to provide sufficient tensile strength.
These closely woven, thick filter sheets have a number of disadvantages. Due to their thickness, their dehydrating efficiency is extremely low and several steps involving pressing drums 4 are required. Ordinarily, as many as 10 pressing steps are involved which result in a large, complicated and expensive dehydration device. To partially increase the dehydrating efficiency of closely woven, thick filter sheets, vaccuum equipment has been installed on the underside of the lower belt 1 to forcibly draw water through the filter sheet. Such additional equipment adds further complication and expense to the devices.
In typical previously known dehydration devices, the belts 1 and 2 are washed with water after the dehydrated cakes A' are scraped off. Due to the closely woven, thick filter sheets of the prior art, a large amount of high pressured water was required to wash the belts. This further reduced the working efficiency of the devices.
In the previously known belt press type dehydration devices using rollers, the concentrated sludge A is not always placed evenly across the width of the belt and, consequently, the belts tend to slip and meander on the rollers 7 and 8 as they progress through the several steps of the pressing drums 4. Accordingly, in these conventional devices, many auxiliary units must be set up in many places and because of this, the devices grew complex.
Finally, the cost of replacing the previously known closely woven, thick filter sheet belts was relatively expensive and the necessity of changing wasted belts made operation of the device costly.